Pretty solid advice to carry with you as a freelancer!
If you’re a freelance designer, or you work for another company, you got there not because you love business, but because you’re a designer at heart. The business side of things came as a necessary evil, but you really love nothing more than to doodle all day, mess around in photoshop, or bang out semantic code. There are a lot of traits of being a good designer which are counter-intuitive to being a good business person. But if you learn to embrace both sides of the coin, your business will prosper, and you’ll get to do more design.